1. Field of the Invention
This invention relates generally to a differential mechanism for use with a vehicle transmission.
2. Description of the Prior Art
In a typical automotive axle application, a differential case is supported within a differential housing. Differential gears interconnect a prop shaft of the vehicle to a vehicle transmission of a vehicle. The differential gears further connect axle shafts which extend from the differential housing to the rear wheels. Thus, power is transferred from the vehicle transmission, through the drive shaft, through the differential case, and to the wheels of the vehicle. Differential mechanisms are used in vehicle transmission to transmit torque from a transmission output to opposing axle shafts allowing right and left wheels to rotate at different speeds, particularly important when negotiating a turn.
While performing generally the same function, differential mechanisms have different dimensional requirements for rear wheel and front wheel drive vehicles. Specifically, differentials intended for use on the front wheel drive vehicles require a beveled, and even annular shape in order to compensate for both the smaller packaging area available and to account for the steering characteristics of the front wheels of the vehicle. The rear wheel drive vehicles are typically larger and require more torque production than front wheel drive vehicles and include sport utility, pick-ups, and even heavy duty vehicles. Therefore, the rear wheel drive differential is typically dimensioned larger with heavier gauge steel than is a front wheel drive differential.
Iron castings presently used to form the housing of a differential for the rear wheel drive vehicle requires a large number of machining operations to produce finished parts having the dimensions necessary to provide adequate tolerances to support the gears disposed within the housing. Dimensional accuracy is important to produce a vibration free motion of the differential in order to produce a smooth vehicle operation. Given the high torque requirements that is typical of the rear wheel drive vehicle, it is believed that the differential housing should include a more dimensionally stable and durable configuration than what is required of a front wheel drive differential housing. Furthermore, many of the manufacturing drawbacks of cast differential housings have resulted in excessive cost of the typical vehicle transmission.
The art is replete with various designs and methods of forming a differential housing using a cold flow-forming process taught by the U.S. Pat. No. 6,045,479 to Victoria et. al; U.S. Pat. No. 6,061,907 to Victoria et. al.; U.S. Pat. No. 6,176,152, and U.S. Pat. No. 6,379,277 to Victoria et. al. The U.S. Pat. No. 6,045,479 to Victoria et al, for example, teaches a housing for differential mechanism that is formed in two pieces using a cold flow-forming process. Each of the housing portions is formed with an internal hemispherical surface, and U-shaped recesses, which when aligned form circular recesses within which a pinion shaft is seated. A subassembly that includes the pinion shaft, pinion gears, side bevel gears, and a thin plastic liner surrounding the subassembly has to be aligned within the housing before an upper housing portion is inserted within the upper portion and welded. The opportunity remains for an improved alignment and meshing engagement between the pinion gears and the side bevel gears along with improved method of installation of the pinion and side bevel gears.
Alluding to the above, the prior art patents do not provide an improved meshing engagement between the gears as the gears are installed within the differential case. Therefore, there is a constant need in the area of a differential art for improved designs and methods of manufacturing the differential mechanisms that is durable, rigid, and which forms an improved alignment and meshing engagement between the pinion gears and the side bevel gears along with improved method of installation of the pinion and side bevel gears.